The Initial Mass Function of the Galactic Early-type Field Stars Based on the LAMOST Survey

Abstract Research on the high-mass end of the initial mass function (IMF) has been limited due to a scarcity of samples. Recently, Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), as the most efficient spectroscopic telescope, has provided new opportunities for related research. In this study, based on approximately 70,000 main-sequence early-type stars from the LAMOST survey, we investigated the IMF of Galactic field stars at the high-mass end (1.5 ≤ M / M ⊙ ≤ 7.1). First, we derived the slope of the present-day mass function (PDMF), finding <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">pre</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>5.59</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.02</mml:mn> </mml:math> after correcting for selection effect in the observed sample. We then accounted for the effects of stellar evolution and unresolved binaries to correct the PDMF back to the IMF, resulting in α ini = 2.70 ∼ 2.82. Notably, we corrected both stellar evolution and unresolved binary effects simultaneously by using binary-Star evolution code, which enhances the robustness of our results. Additionally, we investigated how different mass-ratio ( q ) distributions of binaries and different star formation histories of the Milky Way impact the IMF. Finally, we tested samples across different spatial scales and found that α ini may exhibit a decreasing trend as the spatial scale increases, which could be attributed to variations in metallicity.